The primary functions of a drilling fluid or mud are: to carry chips and cuttings produced by drilling to the surface; to lubricate and cool the drill bit and drill string; to form a filter cake which obstructs filtrate invasion in the formation; to maintain the walls of the borehole; to control formation pressures and prevent lost returns; to suspend cuttings during rig shutdowns; and to protect the formation for later successful completion and production.
Useful drilling fluids or muds must maintain rheological and viscosity properties under normal operation conditions. Also, the drilling fluids or muds must be able to suspend cuttings and weighting materials upon stopping of circulation of the drilling fluid. It is desirable to have drilling fluids or muds which maintain thixotropy and rheology even with increased solids.
U.S. Pat. Nos. 2,938,016; 2,980,653; 3,085,994; 3,342,787; 3,418,292; 3,451,979; 3,536,461; 3,558,570; 3,702,300; and 3,723,375 relate to carboxy-containing interpolymers, methods of making the carboxy-containing interpolymers, and esters and nitrogen-containing esters derived therefrom.
U.S. Pat. No. 2,977,334 relates to derivatives of ethylene-maleic anhydride copolymers. These polymers are useful as coating resins, synthetic varnish for drying oils, additive for mineral or synthetic oils, paper and textile sizing agents, laminating, casting and potting resins, adhesive agents, waterproofing agents, film-forming polymers and plasticizers.
U.S. Pat. Nos. 3,215,707; 3,219,666; 3,231,587; 3,381,022; 3,522,179; 3,912,764; 4,110,349; 4,234,435 and UK 1,440,219 relate to succinic acylating agents and reaction products of succinic acylating agents and alcohols, amines, or ammonia, and methods of making the same.
U.S. Pat. No. 3,738,934 issued to Broning et al. relates to oil-base drilling fluid compositions, additives and filter cakes which are effective under high temperatures and pressures. The fluid is formed by dispersing particles of an oil and water insoluble vinyl toluene-acrylate copolymer resin in a water-in-oil emulsion drilling fluid.
U.S. Pat. Nos. 3,980,569 and 4,454,059 relate to reaction products of hydroxyaromatic compounds, aldehydes and amines.
U.S. Pat. No. 4,140,640 relates to a self-breaking retarded acid emulsion. The emulsion comprises an aqueous acidizing solution, an oil, an effective amount of an alkyl C.sub.8 -C.sub.18 primary fatty amine and at least one diethanolamide of at least one C.sub.8 -C.sub.18 fatty acid.
U.S. Pat. No. 4,306,980 relates to invert emulsion well servicing fluids. The fluids can be formed by combining a certain oleophilic anhydrides and lime in a water-in-oil emulsion comprising a liquid oleaginous phase and an aqueous phase. The oleophilic anhydrides include alkenyl succinic anhydrides and polymers of alkenyl succinic anhydride, such as alpha-olefin copolymers.
U.S. Pat. Nos. 4,329,249; 4,368,133; 4,435,297; 4,447,348; and 4,448,703 relate to reaction products of a carboxylic acylating agent and a hydroxyamine.
U.S. Pat. No. 4,436,636 relates to invert emulsion well servicing fluids. The fluid comprises a liquid oleaginous phase, an aqueous phase, an emulsifying agent and a solid particulate polyolefin. The emulsifying agent may be a polyamide type formed by the reaction of a polyamine with fatty acids and a dibasic acid.
U.S. Pat. No. 4,526,950 relates to polymers of alpha-olefins and alpha, beta-unsaturated carboxylic acids or derivatives and methods of making these polymers.
U.S. Pat. No. 4,566,978 relates to high temperature drilling fluids. The drilling fluid comprises a water-base, clay suspended in the base and a hydrolyzed terpolymer of maleic anhydride, styrene and a third monomer selected from a acrylamide, methacrylamide, acrylic acid or methacrylic acid.
U.S. Pat. No. 4,708,753 relates to water-in-oil emulsions. The emulsion comprises a continuous oil phase, a discontinuous aqueous phase, at least one salt derived from a hydrocarbyl-substituted carboxylic acid or anhydride, or ester or a derivative of said acid or ester and an amine, and a water-soluble, oil-insoluble functional additive dissolved in the aqueous phase, with a proviso that when ammonium nitrate is the functional additive, then the salt is other than an ester/salt formed from the reaction of a polyisobutenyl (M=950) succinic anhydride with diethylethanolamine in a ratio of one equivalent of anhydride to one equivalent of amine.
U.S. Pat. No. 4,776,966 relates to water in oil emulsion drilling fluid compositions in which a block or graft copolymer, of the general formula (A--COO).sub.m B, where A and B represent polymeric components derived from a specific type of oil-soluble complex monocarboxylic acid and from a water-soluble polyalkylene glycol or polyether polyol, respectively, and m is an integer at least 2, serves as the emulsifier. A surfactant containing a C.sub.30-500 hydrocarbon chain as a hydrophobic component, and a polar component adsorbable on to the particulate solid surface serves as a agent for dispersing solid particulate matter in the oil phase. A particularly useful example of the emulsifier is a copolymer in which each A component is the residue of poly(12-hydroxystearic acid) chain terminated with stearic acid of molecular weight approximately 1750, and in which each B component is derived from polyethylene glycol of molecular weight 1500. This copolymer may be prepared by self condensation of commercial 12-hydroxystearic acid (which already contain a proportion of stearic acid which can function as a chain terminator), followed by reaction of the product with polyethylene glycol in the presence of an esterification catalyst. An example of a preferred dispersant is poly(isobutenyl)succinic anhydride having a molecular weight in the range of 400 to 5000. Optionally the succinic anhydride may be reacted with molecules containing a hydroxyl or an amino group.